Fortran Wall Clock Time

Intel fortran compiler 19 1 developer guide and reference.

Fortran wall clock time. For details see fortran library reference manual or the individual man pages for these functions. Fortran 95 and later class. Getprocesstimes is the only routine to return cpu time while the others return elapsed time. However in a more difficult manor.

Note that time may contain a system dependent arbitrary offset and may not start with 0 0. Get date and time. Time in seconds since an arbitrary time in the past. For use as a timing routine with the speed of modern processors this is a very poor precision to provide.

Notes this is intended to be a high resolution elapsed or wall clock. If no time source is available time is set to 1 0. This is a fortran 77 version of the fortran 90 intrinsic routine and is year 2000 safe. I was not trying to say that cpu time and system clock are the same but that both these fortran standard routines use timing sources that are updated every 1 64th of a second.

Again my experience is limited to the win environment. 9 265 system clock time function description. If the attribute mpi wtime is global is defined and true then the value is synchronized across all processes in mpi comm world. I wasn t able to find it on intel s homepage.

Fortran 95 and later. Then i stumbled across call system clock count count rate count max which seems to do the same thing. It is most often used for measuring or tracking the time spent in code blocks in lieu of using profiling tools. When timing a fortran program i usually just use the command call cpu time t.

Developer guide and reference. The fortran intrinsics are. See mpi wtick to determine the resolution of mpi wtime. Getprocesstimes suffers from poor resolution when i have tested it.

System clock is typically used to measure short time intervals system clocks may be 24 hour clocks or measure processor clock ticks since boot for example. For cpu time the absolute value is meaningless only differences between subsequent calls to this subroutine as shown in the example below should be used. If the platform supports a monotonic clock that clock is used and can depending on the platform clock implementation provide up to nanosecond resolution. My knowledge of these come from.

The date and time subroutine returns data from the real time clock and the date. 07 15 2020 public content download as pdf. Local time is returned as well as the difference between local time and universal coordinated time utc also known as greenwich mean time gmt.